Backers of a gay-inclusive domestic partnership law in Washington State sued election officials Thursday. They claim officials have accepted thousands of invalid signatures from a referendum that would place the law up for a vote.

The political group Washington Families Standing Together alleges Secretary of State Sam Reed has accepted thousands of “defective petitions” and signatures of people who were not registered voters at the time they signed the petitions.

Reed accepted “thousands of signatures on petitions where the required declarations were either left blank, not signed by the person who circulated the petitions or not signed by the declarant,” the complaint says.

“Plaintiffs have received confirmation from the SOS (Secretary of State) that the Secretary has accepted thousands of petitions on which the signature-gatherer who circulated the petition did not sign the declaration.”

“Likewise, the Plaintiffs received confirmation from the SOS that the Secretary was ignoring the requirement that only individuals who were duly registered voters could legally sign petitions.”

The complaint says that Secretary Reed relied on the advice of Attorney General Rob McKenna in his decision making.

Opponents of the gay partner law – dubbed the “everything but marriage” law by the media – submitted 137,689 signatures on July 25 to qualify Referendum 71, which would force a vote on the law. But that's lower than the 150,000 signatures suggested by state officials, giving the petition a tight 12.4 percent margin of error it cannot exceed to qualify.

“Because of the limited number of signatures turned in, failure to enforce these laws could well lead to a measure being qualified for the ballot that should not be, and that measure has the potential to strip away important protections from thousands of families across the state,” the group's chairwoman, Anne Levinson, said in a statement.

A hearing in the case is expected to take place in a King County courtroom next week.

If it qualifies and fails in November, the measure would only repeal rights approved by lawmakers this year, the second time the domestic partnership law has been expanded. Governor Chris Gregoire signed into law the original bill that created the domestic partnership law and the two extensions.

Elections officials said Thursday the signature-checking process will likely be completed by Tuesday.